How do genes turn on and off? If DNA sequence remains unchanged, changes in transcription are caused by differences in DNA-associated factors. So understanding chromatin composition changes within particular regions of DNA is vital to understanding gene expression. This proposal aims to better understand the role of chromatin dynamics in gene expression by examining how ribosomal DNA (rDNA) chromatin composition relates to rDNA transcription in the yeast Saccharomyces cerevisiae using mass spectrometry. This project has three specific aims. The first is to purify native rDNA chromatin from yeast cells. Second, the identity [and locations] of bound proteins and nature of histone modifications will be determined using mass spectrometry. Third, differences in chromatin composition and histone modifications between actively transcribed and silent rDNA will be determined. Future directions include extending the technology from yeast to mammalian cells. Chromatin composition at crucial loci could be followed through developmental transudations, environmental changes, or during oncogenesis. My ultimate goal is the complete characterization of an organism's "chromatome:" the identity, quantity, and location of all proteins associated with every DNA sequence and their modification states through development, aging and disease. [unreadable] [unreadable] [unreadable]